Volvo Md7a Rebuild or Repower

[jeffjd]

Yes too long of a thread.

Yes - Raw water cooled.

I might have to get on electric pump to test.


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[Cheechako]

NAPA has little ones, they were about $20.. not sure now....

[hpeer]

I'm pretty sure my transmission runs cool. Can't say I ever specically looked to know this. But I think I would have known by now.

Maybe some one else can opine on this. My boat is out of the water.

[seadago]

Originally Posted by jeffjd

Seadago,

Are you using the same prop as you had with the md7a? I thought they are different direction engines?


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Hi Jeffjd
Good point!
The beta turns anticlockwise at the axle, though still clockwise at the flywheel, both viewed forward. A fact that I ignored when I bought the engine, and my mechanic (not a Beta specialist) missed altogether. Not that that fact would have dissuaded me from buying the engine in the first place.

From the functional standpoint, the std Beta 16 comes with a Technodrive TCM40 gearbox that has nearly identical ratios: 2:1 forward, 2.13:1 reverse. With the season ending in UK, it does not worry me too much. I run reverse to go forward for the short runs I have to do now, and I'll replace the prop for a feathering one for next season.

[jeffjd]

I have come to the point that I need to call it. One more md7a is dead.

Well it runs half way w/ smoke so will use it until a beta 16 comes in and I have the energy to repower. Seems silly spending $10k on a $15k boat. But I guess spending $6k on slip fees is silly also.

Summary of event:

Blew a head gasket. Head had a worn channel so the the head was welded, surfaced and valve job. Replaced head gasket a twice.

Decked the block with sheet of glass and sand paper. Compression checked out at 340 psi. No leak down test done. Engine starts. Revs to 1500 in gear.

Thought it was fuel so had injector pump checked and injectors. Injectors rebuild. Bypassed ever component of the fuel system to check and replaced every washer and hose. No change, except ran a little better with the rebuilt injectors.

Check the timing, tested advancing and retarding the timing is at its best position.

Checked the entire exhaust system it is clear.

Last night when I installed the alternator I notice that is reduced the revs when in neutral. So the engine really is missing power.

All in all I have spent somewhere around $1500 on a engine that I will part out. Moral of the story.... Be careful if you start working on a raw water penta. Sad thing is I knew this before I started. Even if I pulled the engine changed the rings I still might have the same issue.

Thanks for the comments during this process.


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[barnakiel]

Hi,

Thanks for all info you have posted!!! Most valuable.

We are on MD7 vagon too, similar challenges, same options. We may face the same decisions tomorrow or next year but sure we will.

A shame your engine could not be fixed ;-( A new Beta will be a dream and my neighbour now is in the process (Volvo MD2020 to Beta 16).

I believe you may be able to sell parts of the engine on the web. Do not throw it overboard!

Again, many thanks, most useful thread.

barnakiel

[gjordan]

Sorry to hear it is in its death throws. There wont be any trouble parting it out to other Green Demon owners. And dont forget that many parts are common to MD6/6B, and MD7B. Thanks for sharing all of the information of your struggle. I am sure this thread has helped more than a few owners. Best of Luck. ______Grant.

[jeffjd]

If penta supported the engine still a rebuild could be an option. Well the engine lasted 34 years - that is a good run in my book.

Will not even consider a penta for the repower because of the part prices.


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[hpeer]

Thanks for the date. I'm still puzzled as to the why?

I would not be suprised that the engine loads a bit with the alternator.

I HP is 746 watts, and you are not running near 100% efficiency. At at 1500 you are making only 8 or 9 hp.

[jeffjd]

I don't think i will ever know the why it does not run right.

The lesson I learned is unless you are a mechanic - time and penta parts are to dear to fixed something that ultimately has a limited life.


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[Shawn67]

Any chance you ever took an IR thermometer to the engine while it was running? I bought a Sabre 28 this summer with a MD7A. I ran into a situation that sounds similar to the original post. One time when heading out it turned out I had no power at all. Engine would barely throttle up and had no power. After letting it idle for a couple of minutes I checked it with an IR thermometer and it was obvious that it was only running on 1 cylinder. That really surprised me as it was idling fine and at its regular RPM. Turns out I had a slight fuel leak to one of the injectors that was letting a little air in and that was keeping the injector from firing. Cranking it by hand I could hear that only one injector was firing. Bleeding the injector got it running fine again but it took a bit of throttle before the second cylinder started firing. This ended up being an ongoing problem over the season as I just can't get the pipe sealed well at that injector.

MD7A is certainly a learning engine. The day I brought the Sabre home the injector pump died 1/2 mile from my dock... after motoring for 7 hours straight. Swapping that out took weeks due to corrosion on the inspection cover bolts and poor access in that area. By the end of the season the exhaust manifold was running hot by #2 so I am going to pull it this winter to clean out the water passages. I assume one is clogged up.

Shawn

[BobCom]

Sorry repair didn't work out but wonder if you could give me any advice on removing the head. I have an MD7A in a 1981 Sabre 28 which runs fine but found water in the oil when changing it this last fall. Removed exhaust manifold and, after cleaning, seems OK so, suspecting the head gasket, I have removed the rocker arm cover, rocker arm, intake manifold, injector feeds/bleeds and eight head nuts but can't budge it with what seems like reasonable force (not really excessive). I'd appreciate any advice you might have as to how to get it free.

Thanks,
Bob

[Shawn67]

Bob,

The other thing to check is your water pump. If the water seals fail and the weep hole gets clogged it will force water into your crank case. On my Sabre the water side seal was leaking but the weep holes didn't clog. I ended up with a bunch of corrosion on the inspection cover around the water pump and a couple of bolts that were badly corroded.

There were a couple of version of the water pump used on the MD-7A. Mine has small weep holes in it with simpler seals. There is a later pump that has larger slots between the seals to let water out if needed. My earlier parts engine has this type of pump on it.

Shawn

[hpeer]

Originally Posted by BobCom

Sorry repair didn't work out but wonder if you could give me any advice on removing the head. I have an MD7A in a 1981 Sabre 28 which runs fine but found water in the oil when changing it this last fall. Removed exhaust manifold and, after cleaning, seems OK so, suspecting the head gasket, I have removed the rocker arm cover, rocker arm, intake manifold, injector feeds/bleeds and eight head nuts but can't budge it with what seems like reasonable force (not really excessive). I'd appreciate any advice you might have as to how to get it free.

Thanks,
Bob

Do you have the shop manual?

Eight is the right number of bolts. Just put mine on last week.

[BobCom]

Thanks Shawn,
I think I have the same water pump you do and have rebuilt it twice since buying the boat in 1992. The most recent time was summer before last. The symptom was water dripping (almost a stream) coming out of weep hole. I really should check it now and will do so but it looks fine and has lasted over ten years after first rebuild so sort of discounted it this time (it's a bear to get to on the Sabre 28!).

I do have a hard copy of the MD6A manual and the combined MD6A/MD7A manual as a PDF file but both are pretty confusing regarding removing the head. Both say to remove nine bolts but, finding only eight studs I checked an on-line parts list (european parts) and it shows 8 studs for the MD7A and nine for the MD6A. The combined manual shows a tightening sequence for eight nuts so they seem to intermix instructions for the two engines! One thing that bothers me a lot is they say remove bolts. I hope that does't mean I have to remove the studs as I have removed the eight nuts and I suspect getting the studs out would be a bear!

I'm brand new to this forum and feel guilty adding to this thread but there was so much MD7A expertise here that, given my frustration, I couldn't resist. I will try not to lengthen it any more would still like any information about the last steps of getting the head off.

Thanks,
Bob